fix(deps): update dependency purgecss-webpack-plugin to v6

package.json

@@ -7,7 +7,7 @@
     "html-webpack-plugin": "5.6.0",
     "mini-css-extract-plugin": "2.8.1",
     "prometheus-query": "3.4.0",
-    "purgecss-webpack-plugin": "5.0.0",
+    "purgecss-webpack-plugin": "6.0.0",
     "raw-loader": "4.0.2",
     "webpack": "latest",
     "webpack-cli": "latest",